Lapping machine



y 1969 K. REZNICEK 3,457,679

LAPPING MACHINE Filed Nov. 22, 1966 5 Sheets-Sheet 1 l4 i 76 I! h IINVENTOR K. REZN/CEK ME'QM A T TOHNEVv July 29, 1969 K. REZNICEK3,457,679

LAPPING MACHINE 7 Filed Nov. 22, 1966 s sheets-s eet 2 July 29, 1969 K.REZNICEK 3, 5

7 LAPPING MACHINE Filed Nov. 22, 1966 5 Sheets-Sheet 3 K. REZNICEKLAPPING MACHINE Jul 29, 1969 5 Sheets-Sheet 4 Filed Nov. 22, 1966 July29, 1969- K. REZNICEK 3,457,679

LAPPING MACHINE Filed Nov. 22, 1966 5 SheetsSheet 5 United States PatentOffice 3,457,679 Patented July 29, 1969 US. CI. 51-35 3 Claims ABSTRACTOF THE DISCLOSURE This disclosure concerns a machine for lapping opticalsurfaces in which the lapping bed rotates and also reciprocatees in Xand Y directions. The rotation rate and both reciprocation rates arecontrolled independently.

This invention relates to lapping and polishing machines, andspecifically to a new machine that in the space of a two foot squareautomatically laps to a high degree of flatness and uniformity surfacesof 15-20 inches in diameter.

Certain critical design requirements of new art optics such asdispersive delay lines have been extremely difficult or impossible tomeet with known conventional flatlapping machines. One typicalrequirement for example, calls for a high order of flatness on a givenelongated surface. A second such requirement relates to surfacesmoothness or finish generally characterized by an absence of scores,scratches, or other surface imperfections of even a A. micron in widthand length. These faults must not be detectable under a x magnification.For a variety of reasons, existing lapping technology falls short ofmeeting these and other needs.

For example, the lapping motion produced by known machines is notuniformly applied over the lapped surface. Typically the lapping plateand the surface undergo a relative pivotal movement in which one ispivotally swept across the other as the latter rotates in place.Inevitably, the surface portion farthest away from the pivot point movesand hence is lapped more. The resulting lap is proportionately out offlat even under otherwise ideal conditions. Merely to lengthen the pivotarm and thus minimize this sweep differential is no solution since it isnever quite eliminated; and further, lengthening requires still morespace for a machine that already occupies thirty or more square feet.

A further reason for the failure of prior lapping machines to producethe extreme surface flatness and smoothness now desired is that theirmotions invariably at one point or another introduce a nonrandomness inthe lap. This problem encompasses the one just noted, but is broaderbecause it can stem from a host of causes. One cause is a lingering orhesitation in whatever relative movement exists between lapping plateand surface. If at this time the lapping action is momentarily unequalfor other reasons, the lapping will progress unevenly for the durationof the pause. Another cause is the tendency of the lapping slurry toflow outwardly toward the rim of the lapping plate which makes thelapping rate greater at the rim area. This latter problem is compoundedby the conventional cross-hatch plate groove pattern and further by thereferred-to conventional pivotal movement still so often employed. Othercauses of nonrandomness are prolonged jerky motions and sinusoidalaccelerations and decelerations between plate and surface, and thetendency of known lapping mixtures to agglomerate because ofinsufficient wetting.

It has been possible in the past for a highly skilled optical finisherto produce the desired surface by handfinishing. Herein, however, liescause for further concern with existing lapping technology. There is achronic shortage of such technicians. The skills are esoteric and theirmethods not generally understood. The hand operation literally takesweeks and months to complete. Finally, the experienced yield rate ofsatisfactorily finished surfaces is under 40 percent. Needless to say,the cost per good surface is considerable.

Accordingly, each of the following are important and immediate objectsof the invention:

To produce highly flat, smooth optical surfaces entirely by machine;

To reduce substantially the overall cost of lapping such opticalsurfaces;

To increase the Working capacity of general purpose lapping machineswithout increasing their size;

To eliminate hand-finishing and all other costly labor charges in theproduction of such surfaces;

To cut, in a major way, the time required to produce such surfaces;

To improve, markedly, the yield of satisfactory surfaces generatedduring the lapping and polishing steps; and

To make the outcome of these processes predictable.

These and other objects are achieved pursuant to the invention, broadly,by a lapping bed rotatable at various speeds in its horizontal X-Y planeand also reciprocal at various speeds in both X and Y directions, thework piece being positioned atop the bed and able to rotate with it butrestrained from translational movement.

In one illustrative embodiment described in detail below, the lappingbed supports a circular lapping plate. The work piece-a 12" x /2"substrate quartz surface for eXample-is embedded flush in a second ortop circular lapping plate which rests freely of its own Weight upon thebottom plate. Restraining rollers of rubber or the like are adjustablypositioned at intervals along the circular rim of the top plate.Rotation of the bottom plate will be imparted to the top plate, buttranslation of the bottom plate in its X-Y plane will not be imparted tothe top plate except to the slight degree allowed by the clearancebetween rollers and rim.

Hence, the relative motion between the contacting plate surfaces is acomplex and constantly changing amalgam of lateral and rotationalslippage. The resulting lap and polish is benefited in several ways.First, there is nothing akin to the objectionable pivot-arm movementcharacteristic of the earlier machines. Second, the relative platemovement follows a completely nonrecurring pattern, as the followingwill illustrate. Starting at a rand-om time and with bottom and topplates in a given juxtaposition each with a given angular velocity andwith the bottom plate undergoing certain X and Y velocities, thelikelihood that the plates will return even once in a finite cycle tothe same juxtaposition and thereafter undergo the same relative movementsequence as occurred earlier, is infinitesimally small. For this reasonalone, a very high degree of random or nonrecurring relative movement isassured, which contributes importantly to achieving the flat, smoothsurface desired.

The random plate movement is further enhanced in accordance with anotheraspect of the invention by programming the bottom plate for certainangular velocities and also X and Y velocities or reciprocating rateswhich have been ascertained in advance to maximize the randomness of themovement. There doubtless are many such combinations and some have beenfound empirically. The whole range, however, requires computercalculation.

Additionally, by retarding the rotation of the upper plate periodicallyfor brief intervals by a braking mechanism, a further improvement of thefinal quality of the lapped surface is achieved in some specialinstances. Such retardation will occur each time the bottom platereaches the limits of the X position and cause about a tenth of a radianslippage each time.

A further aspect of the invention concerns mechanisms by which the X andY movements are quickly and smoothly reversed at the extremes of areciprocation. The problem of lingering and sinusoidal speed variationsearlier referred to thus becomes de minimus. The same mechanism assuresa constant X or Y velocity during a stroke which prevents the jerky orjittery movements.

The sought-after quality of lap is realized through two further highlydesirablealthough not necessary-adjuncts to the invention. It has beenfound that the lapping plate is more effective when employing circulargrooves cut in a specific pattern upon the surface of the lapping plate.This pattern comprises, generally, six such grooves evenly spaced toform an inner circle with its center as that of the plate, and 13similar grooves similarly spaced to form an outer concentric circle. Thebasic generator matrix for all grooves is an equilateral triangle.Secondly, a foundation of lapping slurry not heretofore employed hasbeen found particularly resistant to agglomeration, a problem which hasplagued earlier eiforts to produce eventextured laps.

One feature of the invention, accordingly, resides in a bottom lappingplate which rotates and translates at selectable speeds, and a toplapping plate containing the surface for lapping that rests freely uponthe bottom plate and rotates with it but does not translate with it.

Another feature of the invention concerns a quick-reverse mechanism toenhance the reciprocating movements of the bottom plate.

A further feature of the invention lies in the independent speedcontrols for all movements of the bottom plate.

A general feature of the invention relates to the capability of themachine to be set initially and thereafter perform all lapping necessaryto achieve the desired surface.

These and other objects and features of the invention are made evidentin the description to follow of an illustrative embodiment and in thedrawing in which:

FIG. 1 is a frontal perspective of the machine;

FIG. 2 is a schematic diagram of the lapping bed mountrugs;

FIG. 3 is a side view of the mountings;

FIG. 4 is a front view of the mountings;

FIG. 5 is an exploded front perspective of the lapping bed and plates;

FIG. 6 is a schematic mechanical and electrical diagram of the drivemeans for the lapping bed;

FIG. 7 is a schematic diagram showing the translational reversing means;

FIGS. 8 and 9 are schematic diagrams showing a lap piece mounted in thetop plate; and

FIG. 10 is a top view of a lapping plate.

STRUCTURE The overall lapping machine is illustrated in FIG. 1 anddesignated as 10. All the components are mounted on a table stand 11with a flat top surface 12 having a cutout midsection designated 13 asshown in FIG. 2. Surface 12 embraces the entire area in which thelapping machine 10 functions, being typically no more than 24 inches ona side.

Mounted on opposite sides of surface 12, as shown in FIGS. 1 and 2, aretwo blocks 14, 15. These provide a slidable mount in an X direction, asdesignated by the arrow 16, for a frame consisting of slide bars 17, 18,19, and 20. Four angle blocks 21 secure together the end portions of theslide bars in rigid fashion. As seen in FIG. 2, block 14 slidably mountson bar 17, and block 15 slidably mounts on bar 18.

Two other mounting blocks 22, 23 are slidably accommodated on slide bars19 and 20, respectively. Whereas blocks 14 and 15 are attached tosurface 12 as shown,

for example, in FIG. 3, blocks 22, 23 are disposed above surface 12 asseen in FIG. 4. A circular plate 24 is attached rigidly at its peripheryto mounting blocks 22, 23, as shown in FIG. 2.

Plate 24 supports an undercarriage 25, as seen in FIGS. 2 and 5.Undercarriage 25 comprises a vertical shaft 26 driven by two motors 66,67 in a manner to be described, and four harness bars 27a, 27b, 27c, and27d rigged outwardly on each of the four sides of undercarriage 25. Aone piece belt 28, as seen in FIG. 2, is drivably attached to harnessbars 27a and 27c; and a second one piece belt 29 is drivably attached toharness bars 27b and 27d.

It is seen from the foregoing that motion for undercarriage 25 in the Xdirection as indicated by arrow 16 is effected by movement of belt 28 inthe X direction. Similarly, movement of. undercarriage 25 in the Ydirection as indicated by arrow 30 is effected by movement of belt 29which draws blocks 22 and 23 in sliding movement along their respectivebars 19, 20. In addition to this X and Y direction movement, it is seenthat simultaneously shaft 26 rotates.

A suitable bearing such as 30 is employed to insure that shaft 26 has noradial or axial play with respect to plate 24, but is supported thereonfor smooth rotation. An end flange 31 attached to shaft 26, as seen inFIG. 5, is adapted to mount a circular lapping bed 32 which receives alower lapping plate 70. Lapping plate is positively coupled to thebottom surface of bed 32 through a coupling disc 34 that maintains plate70 symmetrically around the vertical axis of shaft 26.

In accordance with a main facet of the invention, both the speed and thestroke length of undercarriage 25 in the X direction and in the Ydirection can be varied. The structure that effects this result will nowbe described.

A number of structural struts, shown in FIG. 6 and designated 33, 34,35,36, 37, 38, 39, and 40, are constructed integrally with table stand 11.One pair of struts, for example 35, 36, is associated with each of thefour sides beneath top surface 12. The apparatus which each of thesestrut pairs such as 35, 36 supports is substantially identical instructure and function. In the description to follow, like numbers referto like parts, but are distinguished as to their location by lettersuffixes.

As seen in FIG. 6, a shaft 41a is mounted in strut 35 for rotationalmotion which is imparted to it through a gear box in strut 35 (notshown) by a drive belt comprising pulley 42a, belt 43a, pulley 44a,drive shaft 450, and motor 46a. Pulley 44a and motor 46a are mounted bysuitable means (not shown) rigidly to table stand 11. On shaft 41a thereis mounted a magnetic clutch 47a which connects and disconnects shaft41a with another shaft 48a. Shaft 48a is mounted in strut 36 inalignment with shaft 41a. A drive pulley 49a is secured to theapproximate center of shaft 48a; and, as seen in FIG. 7, at the end ofshaft 48:: is mounted a disc 50a with a mirror 51a. Facing disc 50a is asecond disc 52a mounted on a shaft 53a that is positionable throughpulley 54a, belt 55a, drive pulley 56a, and motor 57a. Motor 57a, aswell as shaft 53a, is rigidly secured by means (not shown) to theunderside of table stand 11. A photocell 60a is mounted on disc 52a andinteracts with mirror 51a in a manner described later.

A positively-loaded idler pulley 58a tensions belt 28 which feeds overdrive pulley 49a and attaches to harnesses 27a, 27c by end members 59a,59c. The latter ride in ball bearings along harness bars 27a, 27c.

Each of the above-described components 4112 through 59a havecounterparts 41b through 5% associated with strut pair 37, 38; 41cthrough 590 associated with strut pair 39, 40; and finally 41d through59d associated with strut pair 33, 34. The description given above withrespect to the interrelationships and structure of components 41athrough 59a applies exactly with respect to each of the other three setsof like-numbered components. Their operational interrelationships willbe described in detail below.

Another magnetic clutch, designated 78 in FIG. 1. is supported on arigid shaft 79 suspended by some su1table means, such as support frame80, above the upper lapping plate 74. Clutch 78 can be fastened bywellknown gimbal mechanisms (not shown) to upper plate 74, by loweringit downwardly on frame 80. An electrical connection 178 is made betweenclutch 78 and control unit 61 which contains means (not shown) forintermittently engaging clutch 78 automatically. When so engaged, clutch78 momentarily stops the sympathetic rotation of upper plate 74, forperhaps two or three degrees. This action is a further randomnessavailable for inclusion in the lapping program and contributes inspecial cases to the desired surface uniformity in the end product.

Suitable electrical interconnections 146a, 147a, and 157a are providedbetween a control unit 61 and motor 461:, clutch 47a, and motor 57a. Inlike manner, electrical connections 146b, 1471) and 157b to control unit61 are effected for motor 46b, clutch 47b and motor 57b. Similarlyconnections 146e, 147a, and 1570 are effected respectively between motor46c, clutch 47c and motor 570 and the control unit 61. Also, connections146d, and 147d, and 157d are effected between motor 46d, clutch 47d, andmotor 57d and the control unit 61. In addition, electrical connection166 is effected between unit 61 and motors 66, 67. Finally, photocell60a as well as photocells 60b, 60c, and 600! are positively connectedthrough arrangements (not shown) via connections 160a, 160b, 160s, and160d respectively to control unit 61.

OPERATION The stroke and speed in the X direction may both be variedindependently of one another and also of all other motion'undergone bylapping bed 32. Certain other supporting features of the invention comeinto play in the etfectuation of this motion to insure smooth movementsas wellas smooth transitions. The manner of achieving X movement andstroke is identical to the manner of achieving Y movement and stroke;and accordingly only the X movement will be described, it beingunderstood that the description applies equally to movement in the Ydirection.

The description to follow is taken in conjunction with FIGS. 6 and 7. Itwillv be noted that mirror 51a is mounted on the periphery of disc 50a.Accordingly, mirror 51a undergoes an angular displacement equal to theangular displacement of .pulley 49a, which is mounted on the same shaft48a. In turn, pulley 49a undergoes a total angular displacementdependent on the X direction freedom of movement of belt 28 to which, ofcourse, undercarriage 25 is attached. The limits of the X displacementundergone by carriage 25 thus relate to the angular displacement ofmirror 51a.

As seen in FIG. 7, the photocell 60a includes a light transmittingportion 62a and a light receiving portion 63a. The angular position ofphotocell 6011 may be varied within prescribed limits by adjusting ofthe motor 57a through rheostat 64a in control unit 61.

In accordance with the invention, the diameter of drive pulley 49a canbe chosen with respect to the total X direction displacement of carriage25 so that pulley 49a rotates less than 360 degrees as undercarriage 25traverses its entire X displacement. Accordingly, in this instance theangular displacement of mirror 51a on disc 50a is less than 360degrees-say for illustration purposes, 270 degrees. As a consequence, ifmirror 51a begins its angular rotation from a point where it is inalignment with photocell 60a, then at the end of its angulardisplacement 270 degrees later, mirror 51a will be 270 degrees removedfrom photocell 60a. In the same period, undercarriage 25 has translatedfrom its extreme desired positive X position, as it were, to its extremedesired negative X position. During this interval, pulley 49a undergoesrotation in response to the movement of belt 28. If the diameter ofpulley 490 is the same as that of pulley 49a, then each will bedisplaced an equal angular amount for a given movement of carriage 25,in this case 270 degrees. Additionally, in this case the two mirrors 51aand 51c will undergo the same angular displacement for a given movementof carriage 25, in this case again 270 degrees.

Let it now be assumed that, at the extreme desired point of travel ofundercarriage 25 in the negative X direction, mirror 51c and photocell600 are in alignment. As with photocell 60a and mirror 51a, a lightsignal transmitted by light transmitting portion 620 will be reflectedby mirror 510 back to light receiving portion 630. At this point ofalignment a signal is thus generated. Similarly, a signal is generatedwhen mirror 51a is in angular alignment with photocell 60a at the limitof travel of carriage 25 in the positive X direction. Accordingly, twosignals are generated representing the extremes of travel of carriage 25in its X direction of movement. These signals are turned to advantage inthe manner now to be described.

Magnetic clutches 47a and 470 are engaged and disengaged in response tosignals received from control unit 61. Whether engaged or not, themotors 46a and 460, and their associated belt, pulley and gear drivingtrain, are continuously driving the drive side of each clutch 47a and470. The rotational direction of clutch 47a is such that when engagedwill drive belts 28 in the plus X direction; and the rotationaldirection of clutch 47:: is such that when engaged will drive belt 28 inthe minus X direction. By means of relay switches (not shown) in controlunit 61, magnetic clutch 47a is disengaged in response to the occurrenceof a signal between photocell 60a and mirror 51a upon the occasion oftheir coming into alignment. In response to the same signal, and also bymeans of relays (not shown) in control unit 61, magnetic clutch 47cwhichis disengaged while undercarriage 25 is moving in the positive Xdirection, is engaged simultaneously with the disengagement of clutch47a. The force vector applied to undercarriage 25 thus changes from aplus direction to a minus direction, as drive motor 57c picks up theload. Travel in the minus X direction for undercarriage 25 continuesuntil mirror 51c comes into alignment with photocell 60c. At the pointof alignment, a signal is generated in photocell 600. In response tothis signal, again by means of relays (not shown) in control unit 61,clutch 470 is disengaged and simultaneously clutch 47a is engaged.Movement of undercarriage 25 in the minus X direction is immediatelyarrested, and movement in the plus X direction is commenced.

This oscillatory movement in the X direction of undercarriage 25continues between the limiting points described above, as determined bythe amount of travel allowed undercarriage 25 before alignment of aphotocell with its respective mirror occurs. It has been found desirableto provide a total X direction displacement of approximately four inchesto achieve the lapping motions pursuant to the invention when using alapping plate of about twelve inches in diameter. Obviously, this strokecan be varied to whatever amount is desired, by means, for example, ofvarying the diameter of drive pulleys 49a and 490. Additionally, it isobvious that a 11 rotation ratio between pulley 49a and disc 50a, asdescribed above, can be varied by conventional means such as reductiongears to achieve a stepped down ratio so that disc 50a will rotateproportionately less than pulley 49a. A longer stroke length for thesame angular displacement of disc 50a with respect to photocell disc 52aaccordingly is possible.

Pursuant to a further important aspect of the invention, it is possibleto vary the stroke length of undercarriage 25 in either direction of itsX direction travel, simply by adjusting the angular position at whichthe mirrors come into alignment with their respective photocells.Suppose, for example, that as above, disc 50a and its mirror 51a hastraveled a full 270 degrees away from photocell 60a during the movementof undercarriage 25 in the negative X direction. If now photocell 60a isturned a number of degrees toward mirror 51afor example, 90 degrees thenin the rotational return movement of disc 50a as undercarriage 25 movesin the plus X direction, the alignment of mirror 51a in photocell 60awill occur after disc 50a has rotated 180 degrees instead of 270degrees. Thus the signal generated between photocell 60a and 51a willoccur earlier; and in response to this the reversing of direction ofundercarriage 25 will occur earlier. In accordance with the invention,the precise point at which undercarriage 25 reverses from a positive Xdirection to a negative X direction can be chosen to be any point in itsX direction travel simply by realignment of photocell 60a with respectto mirror 51a. Similarly, by readjusting the position of photocell 600with respect to mirror 510, it is possible to select the precise pointat which undercarriage 25 will reverse from negative X movement tomovement in the positive X direction.

The angular position of photocells 60a and 600 is adjusted through themotors 57a and 570, respectively, which are controlled by rheostatcontrols 65a and 650, respectively. It is also possible to vary thespeed of drive motor 46a and 460 so that they run faster or slower or atthe same or different speeds.

All of the foregoing description with respect to the X directionmovement of carriage 25, applies exactly to the Y direction of movementof carriage 25 except that, of course, the parts with b and dsubscripts, as shown in FIG. 6, are used, All of the variations andadjustments of the stroke of undercarriage 25 provided for the Xdirection are provided in exactly the same method for the Y direction.

Pursuant to another aspect of the invention the planes of operation ofboth belts 28 and 29 are fixed, although undercarriage 25 translates inboth X and Y directions. The end members 59a and 59c of belts 28 areprovided with ball bearings (not shown) which ride along the rods 27aand 270 respectively. Thus, as undercarriage 25 translates in a Ydirection, the aforementioned rods slide within the ball bearings of endmembers 59a and 59s. The extremes of movement in the Y direction are setin the embodiment described by the travel which the mountings of rod 27aon undercarriage 25 will allow before they contact end piece 59a. In thesame fashion, end pieces 59b and 59d ride in ball bearings (not shown)upon rods 27b and 27d, respectively, as undercarriage 25 translates inthe X direction. The same restrictions as to extremes in movement applyhere also.

It is desirable in promoting smooth vibration-free translationalmovement, that the nondriving clutch at a given moment, for example 47c,drag slightly against the driving clutch-47a in this instanceso that thedriving or upper portion of belt 28 is always under tension. This isachieved in the magnetic clutches themselves simply by causing a certainadjustable residual magnetism to occur in the nondriving clutch, as thedriving clutch is fully engaged.

Shaft 26 is driven by two worms mounted in undercarriage 25 which inturn are driven by two separate motors 66 and 67. These motors are setto rotate at slightly different speeds so that one motor is alwaysdragging on the other. In this fashion, any backlash between shaft 26and its two drive worms is substantially eliminated and a smoothcontinuous rotation of shaft 26 thus is promoted. As earlier noted,motors 66 and 67 are powered and controlled from control unit 61 throughelectrical connection 166 and rheostat 68. At all rotational speeds,however, one motor is dragging against the other. There are never anyabrupt or jerky motions in shaft 26 as a consequence.

It is desirable that belts 28 and 29 be of the type that have grippingteeth on their inner edges, so that the chance of slippage occurringbetween the belt and its drive pulleys is eliminated,

8 LAPPING Lapping of surfaces is achieved in the following fashion. Alower lapping plate is placed as described in bed 32. Lapping plate 70is provided advantageously with a pattern of circular grooves such asshown in FIG. 10. This pattern is characterized by a maximum possiblenumber of these grooves for a given lapping plate, none of thesegroovesbeing intersected by the periphery of this given plate, thecenters of these grooves lying on equal equilateral triangles, and thewidth and depth of these grooves being specific for a given lappingplate. An article such as 71 seen in FIGS. 8 and 9 includes a surface 72which is to be lapped, Surface 72 accordingly is embedded in a secondlapping plate 73 which also has a pattern of circular grooves similar tothat of lapping plate 70. The circular grooves help to keep the lappingslurry evenly distributed. Surface 72 is flush with the lapping surfaceof plate 73, as shown in FIG. 9. Good lapping practice also calls for athird lapping plate 74, shown in FIG. 5.

A suitable lapping compound is applied to the lapping surface oflowerplate 70, and lapping plate 73 with its surface 72 to be lapped, isplaced face downward on lapping plate 70. Its weight is supportedentirely by lapping plate 70. Four arms designated 75 are adjustablymounted in supports 76, which are spaced degrees apart upon the surface12 of, table 11. Each arm 75 mounts a rotatable rubber .wheel 77 thatcontacts the vertical surface of the lapping plate which rests on lowerplate 70. The purpose of the arms 75 and wheels 77 is to restrictlateral movement of the upper lapping plate while lower plate 70 istranslating in X and Y directions.

The clutch drive motors 46a, 46b, 46c, 46d are turned on and shaft drivemotors 66, 67 actuated, all from control unit 61. The stroke in the Xand Y directions of undercarriage 25'is set in the manner describedabove. From this point on, lapping occurs entirely automatically and ina completely random but uniform pattern.

Importantly, all three motions contributing to the lapping are performedby=movement of lower plate 70 with respect to the relatively fixed upperplate, the advantages of which are several fold: It is possible in thisscheme to perform a lap on any odd sized shape such as, for example, thetriangular shaped article 71. The lapping is not limited merelyto.flats. Secondly, all of the lapping forces on the plates have veryslight moment arms associated therewith. There are no moment arms whichtend to cause a top plate to .dig an edge into the bottom plate.Further, a fifteen inch surface can be lapped and polished in accordancewith this invention in the space of a two foot square, whereas in priorart machines, at least a twelve foot space was-required. Mostimportantly, it is possible to generate, by this invention, without anydependence on the skill of technicians, the most precise flat surfacesknown, i.e., the optical flats.

It should be noted that the stroke limits can be varied pursuant to theinvention while the machine is in operation. In prior art machines itwas generally necessary to stop the lapping operation if an adjustmentin stroke were desired. Any such interruption in a lapping operationtends to generate scratches or unevenness, which severely handicap thecapability of a machine to produce smooth surfaces.

It has been found highly advantageous to employ in connection with theabove-described invention a lapping compound consisting of the followingmaterials and proportions: One pound abrasive grain such as aluminumoxide; one pound medical grain talcum powder; one cc. aerosol OT (sodiumdioctylsulfosuccinate); and two pounds water. The working batch isproduced of ten percent basic slurry and 90 percent water. The aerosolOT acts as a wetting agent for the abrasive compounds, allowing them tospread uniformly across the work surface without agglomerating andcausing gouging to the Workpiece.

It is to be understood that the invention as defined in the claims tofollow is not limited to the embodiments discussed, which are purelyillustrative; but rather is intended to cover also the many obviousmodifications and variations that will occur to those skilled in theart.

What is claimed is:

1. Lapping apparatus comprising a lower lapping plate,

a bed for supporting said lower plate,

means for rotating said bed, and

means for reciprocating said bed in an X direction and in a Y direction,

means for limiting the X direction and the Y direction reciprocations ofsaid body,

means for effecting changes in both said limiting means While said Xdirection and said Y direction reciprocations are occurring,

an upper lapping plate including means for flush mounting therein asurface to be lapped,

said upper plate resting freely upon said lower plate and rotating inresponse to rotation thereof, and means for restraining translation ofsaid upper plate.

2. Apparatus pursuant to claim 1, further including References CitedUNITED STATES PATENTS 2,195,065 3/1940 Wallace 51-56 X 3,225,492 12/1965Day et a1. 51-3 749,961 1/ 1904 Fischer 51-3 2,991,594 7/1961 Brown etal. 51-59 3,015,914 1/1962 Roney 51-59 X 1,963,884 6/1934 Budd 51-3JAMES L. JONES, J 11., Primary Examiner US. Cl. X.R.

